Method for controlling an electrochemical system and associated electrochemical system

Abstract

Method for Controlling an Electrochemical System and Associated Electrochemical System. The present invention relates to a method for controlling an electrochemical system (10), comprising: opening a purge valve (41), allowing an anodic outlet gas from a fuel cell (20) to a cathodic inlet (36) of an electrochemical filter (35); and measuring a filter cathodic pressure. The method further comprises the following steps: opening a cathodic valve (42) when the filter cathodic pressure is less than or equal to the first pressure threshold; and opening a fluidic control device (43) when a pressure (P38) measured at the filter anodic outlet (38) is greater than a second pressure threshold. The first pressure threshold is between a fuel cell outlet cathodic pressure and a fuel cell outlet anodic pressure. Figure for the abstract: Figure 1

Description

Title of the invention: Method for controlling an electrochemical system and associated electrochemical system

[0001] The present invention relates to a method for controlling an electrochemical system and an associated electrochemical system. During operation of a fuel cell, not all of the supplied reactive gas, in particular hydrogen, is consumed. It is known to fluidically connect the fuel cell to a recirculation circuit in order to recycle the hydrogen leaving the fuel cell and circulate it again in the cell.

[0002] US2013071763A1 discloses a fuel cell system, comprising several sections, one of the sections being adapted to operate as a hydrogen filter, also called an electrochemical filter or hydrogen pump, and the other sections being adapted to operate as fuel cells. The section operating as a hydrogen filter is integrated into a hydrogen recirculation loop and the power supply of the section operating as a hydrogen filter depends on the hydrogen partial pressure of the gas circulating in the recirculation loop.

[0003] DE102019214288A1 discloses a hydrogen pump, used to filter gas in output of an anode of a fuel cell. The power supply to the pump, as well as the supply of gas to the hydrogen pump and the evacuation of gas after filtration, is intermittent and based on the partial pressure of hydrogen upstream of the hydrogen pump, detected by a pressure detector.

[0004] JP2005268056A discloses a hydrogen pump, which filters gas at the outlet of a Anode of a fuel cell. The hydrogen pump is powered by direct current if the pressure of a gas present in a tank upstream of the hydrogen pump is higher than a threshold pressure. In this case, the hydrogen pump filters the gas in the tank. The filtered gas is then reinjected into the fuel cell, and the residual gas is evacuated.

[0005] These systems are however difficult to supply with electricity without risking rapid damage, particularly when the hydrogen supply is intermittent. Indeed, hydrogen pumps must be electrically supplied to operate, but risk being damaged if they are supplied with electricity in the presence of an insufficient quantity of hydrogen. It is also difficult to determine precisely the quantity of hydrogen received by the hydrogen pump, particularly because the hydrogen contained in the gas to be filtered by the hydrogen pumps is present at high concentrations. It is possible to supply a hydrogen pump hydrogen continuously, but this generates significant electricity consumption.

[0006] The aim of the invention is therefore to propose an electrochemical system which is easy to use, which is less subject to deterioration and which has low electrical consumption.

[0007] To this end, the invention relates to a method for controlling an electrochemical system, the method comprising at least the following steps: - opening a purge valve, allowing a cell anode outlet gas to flow from a cell anode outlet of a fuel cell to a filter cathode inlet; - measurement of a filter cathodic pressure; - electrical supply of the electrochemical filter by an electrical supply device, when the filter cathodic pressure is greater than a first pressure threshold, so that the electrochemical filter dissociates the anode outlet gas of the cell into hydrogen and undesirable cathodic effluents; and - stopping the power supply to the electrochemical filter by the power supply device, when the filter cathodic pressure is less than or equal to the first pressure threshold.

[0008] According to the invention, the method further comprises the following steps: - opening a cathode valve to connect a filter cathode outlet to a fuel cell stack cathode outlet, when the filter cathode pressure is less than or equal to the first pressure threshold in order to evacuate the undesirable cathode effluents; and - opening a fluidic control device to connect the filter anode outlet so that hydrogen flows from the filter anode outlet to the cell anode inlet, when a pressure measured at the filter anode outlet is greater than a second pressure threshold.

[0009] Also according to the invention, the first pressure threshold is between a battery outlet cathodic pressure and a battery outlet anodic pressure.

[0010] An idea underlying the invention is to measure the filter cathodic pressure and compare it to the first pressure threshold, between a cell outlet cathodic pressure and a cell outlet anode pressure, in order to determine whether the electrochemical filter must be supplied with electricity or not. The first pressure threshold is chosen to ensure a circulation of gases compatible with the operation of the system, while allowing a compromise between a purity of the hydrogen supplied by the electrochemical filter and a quantity of hydrogen contained in the undesirable cathodic effluents at the cathodic outlet of the filter and which has therefore not been filtered, which is low. In addition, the opening of the cathodic valve and the control device fluidic when the filter cathodic pressure is higher than the first pressure threshold allows regular evacuation of unwanted cathodic effluents from the filter, containing a small quantity of hydrogen which has not been filtered, limiting the risks of contamination of the filtered hydrogen by unwanted cathodic effluents, and vice versa, this contamination being due to diffusion phenomena through the electrochemical filter.

[0011] According to other advantageous aspects of the invention, the control method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0012] - the filter cathodic pressure is a filter inlet cathodic pressure, measured at the cathode input of the filter;

[0013] - the filter cathodic pressure is a filter outlet cathodic pressure, measured at the cathode output of the filter;

[0014] - the first pressure threshold is equal to the sum of the output cathode pressure of the battery and the difference between the cathodic pressure at the battery outlet and the anodic pressure at the battery outlet, the difference being multiplied by an efficiency criterion of the electrochemical filter;

[0015] - when the filter cathode pressure is greater than the first pressure threshold, the power supply device supplies the electrochemical filter with a constant voltage; and

[0016] - a step of measuring the voltage at the terminals of each of a plurality of cells electrochemical cells of the electrochemical filter and a shutdown of the power supply to the electrochemical filter if the voltage across one of the electrochemical cells is higher than a first voltage threshold.

[0017] The invention also relates to an electrochemical system comprising a fuel cell, the fuel cell comprising a cell anode inlet, a cell cathode inlet, a cell anode outlet and a cell cathode outlet, hydrogen flowing from the cell anode inlet to the cell anode outlet, the system further comprising a cell anode recirculation circuit, connecting the cell anode outlet to the cell anode inlet, the cell anode recirculation circuit comprising a purge circuit comprising a purge valve, and the electrochemical system comprising an anode purge circuit which is fluidically connected to the cell anode outlet, and which comprises a purge valve, the purge circuit comprising: - an electrochemical filter of the proton exchange membrane hydrogen pump type comprising a filter cathode inlet, a filter cathode outlet and a filter anode outlet to which the electrochemical filter delivers filtered hydrogen; and

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] - a cathode valve; in which: - the purge valve is configured to assume an open configuration, in which it connects the cell anode outlet and the filter cathode inlet and allows a cell anode outlet gas to flow from the cell anode outlet to the filter cathode inlet; and - the electrochemical filter is configured to be electrically powered by the electrical power supply device, when a filter cathodic pressure is greater than a first pressure threshold, and configured not to be electrically powered by the electrical power supply device, when the filter cathodic pressure is less than or equal to the first pressure threshold. According to the invention: - the cathode valve is configured to assume an open configuration to connect the filter cathode outlet to a stack cathode outlet of the fuel cell when the filter cathode pressure is greater than a first pressure threshold, in order to discharge unwanted cathode effluents; and - the cell anode recirculation circuit further comprises a fluidic control device configured to assume an open configuration, in which the fluidic control device connects the filter anode outlet and the cell anode inlet when a pressure, measured at the filter anode outlet, is greater than a second pressure threshold, so that hydrogen flows from the filter anode outlet to the cell anode inlet. Also according to the invention, the first pressure threshold is between a battery outlet cathodic pressure and a battery outlet anodic pressure. According to other advantageous aspects of the invention, the system comprises one or more of the following characteristics, taken individually or in all technically possible combinations: - the first pressure threshold is equal to the sum of the cell outlet cathodic pressure and the difference between the cell outlet cathodic pressure and the cell outlet anode pressure, the difference being multiplied by an efficiency factor; - the power supply device is configured to supply the electrochemical filter with a constant voltage; - the fluid control device is a valve; and - a non-return valve downstream of the cathode valve, configured to allow the second gas to flow from the cathode valve to the cell cathode outlet, without allowing the second gas to flow from the cell cathode outlet to the cathode valve.

[0026] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0027] [Fig-1] [Fig.l] is a diagram of an electrochemical system according to the invention;

[0028] [Fig.2] [Fig.2] is a functional diagram of the different stages of a method of piloting according to the invention; and

[0029] [Fig.3] [Fig.3] is a graph representing the evolution of different parameters of the system of [Fig.l] over time.

[0030] A diagram of an electrochemical system 10 is shown in [Fig.l]. The electrochemical system 10 may be integrated into a vehicle, for example to provide electricity for propelling the vehicle. The electrochemical system 10 comprises a fuel cell 20, also called stack 20, a stack anode recirculation circuit 30 and an anode purge circuit 40.

[0031] The fuel cell 20 generally comprises a stack of a plurality of electrochemical cells, not shown. The fuel cell 20 also comprises a cell anode inlet 21, a cell anode outlet 22, a cell cathode inlet 23 and a cell cathode outlet 24. The cell anode inlet 21 is advantageously connected to a gas reservoir containing hydrogen, not shown. The cell cathode outlet 24 advantageously communicates with the exterior of the system 10.

[0032] Gases circulate in the electrochemical system 10, more particularly in the fuel cell 20 and in the cell anode recirculation circuit 30.

[0033] When the system 10 is in operation, hydrogen enters the fuel cell 20 through the cell anode inlet 21 and air enters the fuel cell 20 through the cell cathode inlet 23. At the cell cathode outlet 24, oxygen-depleted air is present, mixed in particular with water in vapor form or in partially liquid form, and a cell anode outlet gas 22, essentially containing hydrogen and nitrogen, is present at the cell anode outlet 22, which then circulates in the cell anode recirculation circuit 30.

[0034] The cell anode recirculation circuit 30 fluidly connects the cell anode outlet 22 to the cell anode inlet 21. In a known manner, the cell anode recirculation circuit 30 has the main function of avoiding the discharge, to the outside, of hydrogen not consumed by the cell 20, by recirculating, to the cell anode inlet 21, the hydrogen not consumed by the cell 20 and which is therefore discharged at the cell anode outlet 22. In a known manner, the anode recirculation circuit 30 comprises a recirculation pump 44 which can be implemented in the form of a motorized pump arranged in the cell anode recirculation circuit 30 or in the form of a venturi ejector.

[0035] The anode purge circuit 40 is connected to the cell anode outlet 22, generally via the cell anode recirculation circuit 30, and comprises a purge valve 41. Preferably, the anode purge circuit 40 is connected to the cell anode recirculation circuit 30 downstream of the recirculation pump. The anode purge circuit 40 makes it possible, when the purge valve 41 is open, to evacuate, from the cell anode recirculation circuit 30, the cell anode outlet gas which contains in particular undesirable fluids such as nitrogen and water. Indeed, due to the anode recirculation by the cell anode recirculation circuit 30, the quantity of these undesirable fluids, other than hydrogen, tends to increase as the recirculation cycles progress.However, it is known that, when the purge valve 41 is opened to evacuate the elements which circulate in the cell anode recirculation circuit 30, not only the undesirable fluids contained in the cell anode outlet gas such as water or nitrogen are evacuated, but also hydrogen which, in the general case, is then lost.

[0036] Preferably, the purge circuit 40 does not open directly outside the system but is preferably connected to the cell cathode outlet 24 so that the undesirable fluids contained in the cell anode outlet gas discharged by the anode purge circuit 40 are mixed with the cathode outlet gases of the cell 20, in particular in order to dilute these undesirable fluids before their discharge outside the system 10.

[0037] To limit the discharge, to the outside, of the hydrogen which is evacuated by the anode purge circuit 40, the anode purge circuit 40 comprises an electrochemical filter 35 of the hydrogen pump type with proton exchange membrane, downstream of the purge valve 41 in the anode purge circuit 40.

[0038] The anode purge circuit 40 advantageously comprises a cathode valve 42, between the cathode outlet 37 of the electrochemical filter 35 and the cathode outlet 24 of the cell 20, a fluid control device 43, between the anode outlet 38 of the electrochemical filter 35 and the anode inlet 21 of the cell 20 and a non-return valve 45, downstream of the cathode valve 42.

[0039] The electrochemical filter 35 comprises at least one electrochemical cell of the hydrogen pump type with a proton exchange membrane and is advantageously a stack of at least two electrochemical cells of the hydrogen pump type with a proton exchange membrane, preferably a plurality of electrochemical cells of the hydrogen pump type with a proton exchange membrane, not shown. The electrochemical filter 35 comprises a cathode 35A, an anode 35B, a filter cathode inlet 36, connected to the cathode 35A, a filter cathode outlet 37 connected to the cathode 35A and a filter anode outlet 38, connected to the anode 35B.

[0040] The electrochemical filter 35 is electrically connected to a power supply device 50. The power supply device 50 is preferably voltage controlled and adapted to deliver a constant voltage to the electrochemical filter 35. For example, the power supply device 50 is a direct voltage generator.

[0041] The purge valve 41 is configured to take an open configuration and a closed configuration. In the open configuration, the purge valve 41 fluidly connects the cell anode outlet 22 and the filter cathode inlet 36, here via the anode purge circuit 40. In the closed configuration, the purge valve 41 fluidly separates the cell anode outlet 22 and the filter cathode inlet 36. Conventionally, the purge of the cell anode recirculation circuit 30 is carried out discontinuously, so that the passage of the purge valve 41 from the closed configuration to the open configuration and then from the open configuration to the closed configuration advantageously takes place regularly.For example, the purge valve 41 moves from the closed configuration to the open configuration, remains in the open configuration for a period of time ranging from 0.1 to 1 second, for example equal to 0.5 seconds, then moves from the open configuration to the closed configuration and remains in the closed configuration for 10 seconds. Alternatively, the purge valve 41 remains in the closed configuration for 5 seconds, or 15 seconds, for example.

[0042] The cathode valve 42 is configured to take an open configuration and a closed configuration. In the open configuration, the cathode valve 42 fluidly connects the filter cathode outlet 37 and the filter cathode outlet 24, through the check valve 45. In the closed configuration, the cathode valve 42 fluidly separates the filter cathode outlet 37 and the passing side of the check valve 45, therefore the filter cathode outlet 24. The cathode valve 42 passes from the closed configuration to the open configuration when a filter cathode pressure Pc is greater than a first pressure threshold PI, called the cathode pressure threshold PI, and from the open configuration to the closed configuration when the filter cathode pressure Pc is less than or equal to the first pressure threshold PL

[0043] The cathode pressure Pc is for example a pressure P37 of a gas at the filter cathode outlet 37. The pressure P37 of the gas at the filter cathode outlet 37 is advantageously measured by a pressure sensor 137 at the filter cathode outlet 37. Alternatively, the filter cathode pressure Pc is a pressure P36 of the first gas at the filter cathode inlet 36. Advantageously, the pressure P36 of a gas at the filter cathode inlet 36 is, for example, measured by a pressure sensor 136 at the filter cathode inlet 36.

[0044] The determination of the first pressure threshold PI will be explained in detail later.

[0045] The fluidic control device 43 is preferably a valve. Alternatively not shown, the second fluidic control device may be another device, such as for example a non-return valve. The fluidic control device 43 is configured to take an open configuration and a closed configuration. In the open configuration, the fluidic control device 43 fluidly connects the filter anode outlet 38 and the battery anode inlet 21, and in the closed configuration, it fluidly separates the filter anode outlet 38 and the battery anode inlet 21.The fluidic control device 43 passes from the closed configuration to the open configuration when a pressure P38 of a gas at the filter anode outlet 38 is greater than a second pressure threshold P2, called the anode pressure threshold, and from the open configuration to the closed configuration when the pressure P38 of the gas at the filter anode outlet 38 is less than or equal to the second pressure threshold P2. This pressure threshold P2 is advantageously a relative pressure threshold with respect to a relative pressure at the cell anode inlet 21, for example of the order of a few millibars. In the case where the fluidic control device 43 is produced in the form of a non-return valve, the latter is arranged to allow the circulation of fluid in a single direction: from the filter anode outlet 38 to the cell anode inlet 21.

[0046] The pressure P38 of the gas at the anode outlet of filter 38 is, for example, measured by a pressure sensor 138. The second pressure threshold P2 is for example chosen to be greater than a pressure of a gas at the anode inlet of battery 21.

[0047] By way of non-limiting example, the value of the pressure threshold P2 can be chosen between 1 and 3 bars.

[0048] The filter anode outlet 38 is connected to the cell anode recirculation circuit 30 downstream of the pump 44, via the fluidic control device 43. The pump 44 fluidly connects the cell anode outlet 22 to the cell anode inlet 21. The pump 44 advantageously serves to increase the pressure of a gas coming from the cell anode outlet 22, such that it is greater than or equal to a pressure of the gas at the cell anode inlet 21. This makes it possible in particular to avoid a circulation of gas in an undesired direction, for example from the cell anode inlet 21 to the cell anode outlet 22. As a variant, not shown, the pump 44 fluidly connects the fluidic control device to the cell anode inlet.

[0049] The non-return valve 45 fluidly connects the cathode valve 42 and the cell cathode outlet 24. The non-return valve 45 allows the circulation of gas from the cathode valve 42 to the cell cathode outlet 24, but prevents the circulation of gas in the other direction, i.e. from the cell cathode outlet 24 to the cathode valve 42. According to a variant not shown, the recirculation circuit 30 does not include a non-return valve 45.

[0050] A method of operation of the system 10 will now be explained, in connection with [Fig. 2]. As mentioned previously, hydrogen enters the fuel cell 20 through the cell anode inlet 21 and air enters the fuel cell 20 through the cell cathode inlet 23. A portion of the hydrogen and a portion of the oxygen in the air react as they pass through the fuel cell 20, thereby generating electricity. Furthermore, gas diffusion phenomena take place in the fuel cell 20, resulting in particular in the mixing of nitrogen, initially present in the air, into the hydrogen circulating in the fuel cell 20. Oxygen-depleted air is present at the cell cathode outlet 24, mixed in particular with water in the form of vapor or in partially liquid form. In addition, the cell anode outlet gas, containing essentially hydrogen and nitrogen, is present at the cell anode outlet 22.

[0051] As long as the purge valve 41 is in the closed configuration, the cell anode outlet gas flows directly from the cell anode outlet 22 to the pump 44 and is reinjected at the cell anode inlet 21.

[0052] The purge valve 41 switches to the open configuration during a step S201. The cell anode outlet gas then flows from the cell anode outlet 22 to the filter cathode inlet 36. The filter cathode pressure Pc increases.

[0053] A step S202 consists of a measurement of the filter cathode pressure Pc and its comparison with the pressure threshold PL

[0054] When the filter cathode pressure Pc is greater than the first pressure threshold PI, a step S203 is performed, in which the electrochemical filter 35 is electrically powered by the power supply device 50. The voltage applied to the electrochemical filter 35 is determined theoretically or after calibration, and depends on the quantity of hydrogen in the cell anode outlet gas. More precisely, a theoretical current is calculated, linked to the pressure of the cell anode outlet gas, the quantity of hydrogen present in this gas and operating parameters of the electrochemical filter 35 such as for example the volume, the temperature, the number of electrochemical cells composing the electrochemical filter 35, etc. according to Faraday's law. The voltage delivered to the electrochemical filter 35 is then deduced from the calculation of the theoretical current.In particular, a voltage that is too high in relation to the quantity of hydrogen in the first gas could damage the electrochemical filter 35. .

[0055] The electrochemical filter 35 dissociates, or filters, the anode cell outlet gas into hydrogen on the one hand and into undesirable cathode effluents on the other hand. More specifically, the electrochemical filter 35 dissociates the dihydrogen present in the anode cell outlet gas at the cathode 35A to form protons, which are then recombined at the anode 35B to form new, more pre-existing hydrogen molecules. dihydrogen. High-purity hydrogen thus accumulates at the anode 35B, and undesirable cathode effluents, essentially nitrogen, accumulate at the cathode 35A. When the electrochemical filter 35 dissociates the anode outlet gas from the cell, the filter cathode pressure Pc decreases and the pressure P38 at the anode outlet of the filter 38 increases. Furthermore, when the electrochemical filter 35 is electrically supplied with voltage by the electrical supply device 50, it is traversed by an intensity I, the value of which is proportional to the filter cathode pressure Pc.

[0056] When the filter cathode pressure Pc is less than or equal to the first threshold PI, a step S204 is implemented, in which the electrical power supply device 50 stops. The electrochemical filter 35 no longer dissociates the cell anode outlet gas. A step S205 is implemented, consisting of opening the cathode valve 42. The undesirable cathode effluents then circulate from the filter cathode outlet 37, i.e. from the cathode 35A, through the non-return valve 45 and to the cell cathode outlet 24 and are evacuated. This makes it possible in particular to prevent the undesirable cathode effluents from remaining too long in the cathode 35A, where they risk diffusing into the hydrogen, thus reducing its purity.

[0057] Steps S204 and S205 preferably take place simultaneously, or partially overlap.

[0058] The non-return valve 45 prevents oxygen from the gas flowing in the battery cathode outlet 24 from entering the electrochemical filter 35 and mixing with the first gas entering the cathode 35A of the electrochemical filter 35. This makes it possible to avoid parasitic chemical reactions in the cathode 35A, and also to avoid the risk of combustion reactions, which can take place when hydrogen and oxygen are mixed. The non-return valve 45 therefore secures the electrochemical system 10.

[0059] A step S210 is then implemented, in which the pressure P38 is measured by the pressure sensor 138 and compared to the second pressure threshold P2. If the pressure P38 is greater than the second pressure threshold P2, a step S211 is implemented. During step S211, the fluidic control device 43 switches to the open configuration, to allow the hydrogen to flow from the filter anode outlet 38 to the cell anode inlet 21.

[0060] If the pressure P38 is less than or equal to the second pressure threshold P2, a step S212 is implemented, in which the fluidic control device 43 switches to the closed configuration. Hydrogen can no longer flow from the filter anode outlet 38 to the cell anode inlet 21.

[0061] Optionally, if the filter cathode pressure Pc is less than or equal to a third pressure threshold, called the safety pressure threshold, a voltage across the terminals of each electrochemical cell of the electrochemical filter 35 is measured. The third pressure threshold is for example associated with an absence of anode cell outlet gas at the filter cathode inlet 36 or at the filter cathode outlet 37. This absence of anode cell outlet gas may be due to a leak, or to a shutdown of the fuel cell 20. The voltage measurement makes it possible in particular to verify that the voltage across the terminals of the electrochemical cells of the electrochemical filter 35 does not exceed a certain predetermined voltage threshold, associated with a malfunction of the electrochemical filter 35. For example, if the voltage across one of the electrochemical cells of the electrochemical filter 35 exceeds the voltage threshold, the electrical power supply device 50 of the electrochemical filter 35 is stopped. This makes it possible to avoid damaging the electrochemical filter 35.

[0062] Alternatively, the voltage across each electrochemical cell can be measured and the electrochemical filter 35 stopped in the event of excessively high voltage across one of the electrochemical cells, i.e. in the event of exceeding the predetermined voltage threshold, independently of the value of the cathodic pressure Pc.

[0063] By way of non-limiting example, the value of the safety pressure threshold can be chosen between 1 and 1.1 bars, for example equal to 1.05 bars.

[0064] By way of non-limiting example, the value of the predetermined voltage threshold can be chosen between 0.1 and 0.5 Volts, for example equal to 0.3 Volts.

[0065] Advantageously, the first pressure threshold PI is greater than the cell outlet cathode pressure P24 and less than the cell outlet anode pressure P22. The values ​​of the pressures P22 and P24 can be measured, respectively at the cell anode outlet 22 and at the cell cathode outlet 24, by sensors comparable to the sensors 136, 137 and / or 138.

[0066] In practice, the values ​​of the pressures P22 and P24 are determined theoretically as a function of the characteristics of the system, such as for example a hydrogen flow rate, a size of the fuel cell 20, etc.

[0067] In a particularly advantageous manner, the first pressure threshold PI is obtained by the following equation:

[0068] P1 = P24 + a(P22 - P24)

[0069] With a an efficiency criterion such that 1-a is an efficiency of the electrochemical filter 35.

[0070] The efficiency criterion a is typically between 0 and 1. When a is zero, the electrochemical filter 35 has perfect efficiency, that is to say that it filters all of the hydrogen present in the anode outlet gas of the cell. Thus, as long as the purge valve 41 remains closed, no additional hydrogen is supplied to the cathode 35A. However, even if there is no hydrogen at the cathode 35A, it is possible that the electrochemical filter 35 continues to be supplied with electricity, for example in the event of a slight delay in cutting off the current, or if the battery anode outlet gas contains less hydrogen than expected. This can cause deterioration of the electrochemical filter 35. When a is 1, the electrochemical filter 35 has zero efficiency, in other words, it does not filter. The battery anode outlet gas admitted into the cathode 35A via the filter cathode inlet 36 is directly discharged to the filter cathode outlet 37, without hydrogen formation at the anode 35B.

[0071] The first pressure threshold PI is therefore obtained theoretically, as a function of the criterion a chosen and the theoretical pressures P22 and P24.

[0072] a is generally chosen to be between 0.02 and 0.1, preferably of the order of 0.05. This makes it possible to filter a sufficient quantity of the hydrogen present in the anode outlet gas of the cell, while limiting the risk of deterioration of the electrochemical filter 35.

[0073] An operating cycle of the system 10, in connection with [Fig.3], is described below.

[0074] During a phase A, the purge valve 41 is closed. The electrical supply device 50 is stopped, the fluidic control device 43 are in the closed configuration. The cathodic pressure Pc is equal to the cathodic pressure of the cell outlet P24.

[0075] During a phase B, the purge valve 41 opens. The filter cathode pressure Pc increases and becomes equal to a maximum filter cathode pressure Pcmax. The maximum filter cathode pressure Pcmax is substantially equal to the cell outlet anode pressure P22, generally to within a few millibars. In [Fig. 3], the maximum filter cathode pressure Pcmax and the cell outlet anode pressure P22 are equal. The maximum filter cathode pressure Pcmax is greater than the first pressure threshold PI, so step S203 is implemented, i.e. the electrochemical filter 35 is electrically supplied with voltage. As a result, the electrical intensity I which flows through the electrochemical filter 35 has a maximum value Imax.

[0076] During a phase C, the electrochemical filter 35 filters the anode outlet gas of the cell to separate the hydrogen from the undesirable cathode effluents, the hydrogen being formed at the anode 35B of the electrochemical filter. Thus the filter cathode pressure Pc decreases and the pressure P38 measured at the anode outlet of the filter increases. The electrical intensity I decreases, proportionally to the filter cathode pressure Pc.

[0077] During a phase D, the pressure P38 reaches the second pressure threshold P2. Step S211 is implemented, and the fluidic control device 43 switches to the open configuration. The formation of hydrogen makes it possible to maintain the pressure P38 equal to the second pressure threshold P2. The filter cathode pressure Pc and the intensity I continue to decrease.

[0078] During a phase E, the filter cathode pressure Pc becomes equal to the first pressure threshold PL. Steps S204 and S205 are implemented, so the electrochemical filter 35 stops, the intensity I becomes zero, and the cathode valve 42 opens, evacuating the undesirable cathode effluents and causing the filter cathode pressure Pc to fall, which becomes equal to the cell outlet cathode pressure P24.

[0079] Since the electrochemical filter 35 is no longer operating, no hydrogen is formed. The pressure P38 decreases and becomes lower than the second pressure threshold P2, causing the implementation of step S212 and the closing of the fluidic control device 43. A new cycle starts, identical to that described previously.

[0080] The electrochemical system 10 described above makes it possible to reuse the hydrogen that has not reacted in the fuel cell 20 and therefore to save it, while having an intermittent power supply. Thus, the electrical consumption of the electrochemical system 10 is lower than that of other systems operating continuously. The cathode valve 42 makes it possible to regularly purge the undesirable cathode effluents and therefore to avoid diffusion phenomena between the hydrogen and the undesirable cathode effluents, which would reduce the efficiency of the electrochemical filter 35. In addition, the first pressure threshold PI can be modified according to the desired performance, by modifying the value of the criterion a, making the electrochemical system adaptable to the requirements of a user and to different contexts of use.

[0081] Any feature described for one variant in the above may be implemented for the other variants described above, as long as technically feasible.

Claims

Claims

1. A method of controlling an electrochemical system (10), the method comprising at least the following steps: - opening (S201) a purge valve (41), allowing a cell anode outlet gas to flow from a cell anode outlet (22) of a fuel cell (20) to a filter cathode inlet (36) of an electrochemical filter (35); - measurement (S202) of a filter cathodic pressure (Pc); - electrical supply (S203) of the electrochemical filter (35) by an electrical supply device (50), when the filter cathodic pressure (Pc) is greater than a first pressure threshold (PI), so that the electrochemical filter (35) dissociates the anode cell outlet gas into hydrogen and undesirable cathodic effluents; and - stopping the electrical supply (S204) of the electrochemical filter (35) by the electrical supply device (50), when the filter cathodic pressure (Pc) is less than or equal to the first pressure threshold (PI); characterized in that the method further comprises the following steps: - opening (S205) of a cathode valve (42) to connect a filter cathode outlet (37) to a cell cathode outlet (24) of the fuel cell (20), when the filter cathode pressure (Pc) is less than or equal to the first pressure threshold (PI) in order to evacuate the undesirable cathode effluents; and - opening (S211) a fluidic control device (43) to connect the filter anode outlet (38) and a cell anode inlet (21) so that hydrogen flows from the filter anode outlet (38) to the cell anode inlet (21), when a pressure (P38) measured at the filter anode outlet (38) is greater than a second pressure threshold (P2); and in that the first pressure threshold (PI) is between a battery outlet cathodic pressure (P24) and an anodic pressure of battery output (P22).

2. A method according to claim 1, wherein the filter cathode pressure (Pc) is a filter inlet cathode pressure, measured at the cathode inlet (36) of the filter.

3. A method according to claim 1, wherein the filter cathode pressure (Pc) is a filter outlet cathode pressure (P37), measured at the filter cathode outlet (37).

4. Method according to any one of the preceding claims, in which the first pressure threshold (PI) is equal to the sum of the battery outlet cathodic pressure (P24) and the difference between the battery outlet cathodic pressure (P24) and the battery outlet anodic pressure (P22), the difference being multiplied by an efficiency criterion (a) of the electrochemical filter (35).

5. A method according to any preceding claim, wherein when the filter cathode pressure (Pc) is greater than the first pressure threshold (PI), the power supply device (50) supplies the electrochemical filter (35) with a constant voltage.

6. A method according to any preceding claim, further comprising a step of measuring voltage across each of a plurality of electrochemical cells of the electrochemical filter (35) and stopping the power supply to the electrochemical filter (35) if the voltage across one of the electrochemical cells is greater than a first voltage threshold.

7. An electrochemical system (10) comprising a fuel cell (20), the fuel cell (20) comprising a cell anode inlet (21), a cell cathode inlet (23), a cell anode outlet (22) and a cell cathode outlet (24), hydrogen flowing from the cell anode inlet (21) to the cell anode outlet (22), the system (10) further comprising a cell anode recirculation circuit (30), connecting the cell anode outlet (22) to the cell anode inlet (21), the cell anode recirculation circuit (30) comprising a purge circuit (40) comprising a purge valve (41), and the electrochemical system comprising an anode purge circuit (40) which is fluidically connected to the cell anode outlet (22), and which comprises a purge valve (41), the purge circuit (40) comprising: - an electrochemical filter (35) of the proton exchange membrane hydrogen pump type comprising an inlet ca- filter cathode outlet (36), a filter cathode outlet (37) and a filter anode outlet (38) to which the electrochemical filter (35) delivers filtered hydrogen; and - a cathode valve (42); in which: - the purge valve (41) is configured to assume an open configuration, in which it connects the cell anode outlet (22) and the filter cathode inlet (36) and allows a cell anode outlet gas to flow from the cell anode outlet (22) to the filter cathode inlet (36); and - the electrochemical filter (35) is configured to be electrically powered by the electrical power supply device (50), when a filter cathodic pressure (Pc) is greater than a first pressure threshold (PI), and configured not to be electrically powered by the electrical power supply device (50), when the filter cathodic pressure (Pc) is less than or equal to the first pressure threshold (PI); characterized in that: - the cathode valve (42) is configured to take an open configuration to connect the filter cathode outlet (37) to a cell cathode outlet (24) of the fuel cell (20) when the filter cathode pressure (Pc) is greater than a first pressure threshold (PI), in order to evacuate unwanted cathode effluents; and - the cell anode recirculation circuit (30) further comprises a fluidic control device (43) configured to take an open configuration, in which the fluidic control device (43) connects the filter anode outlet (38) and the cell anode inlet (21) when a pressure (P38), measured at the filter anode outlet (38), is greater than a second pressure threshold (P2), so that hydrogen flows from the filter anode outlet (38) to the cell anode inlet (21);

8.

9.

10.

11. and in that the first pressure threshold (PI) is between a battery outlet cathodic pressure (24) and a battery outlet anodic pressure (22). The system (10) of claim 7, wherein the first pressure threshold (PI) is equal to the sum of the cell outlet cathode pressure (P24) and the difference between the cell outlet cathode pressure (P24) and the cell outlet anode pressure (P22), the difference being multiplied by an efficiency factor (a). System (10) according to any one of claims 7 or 8, wherein the power supply device (50) is configured to supply the electrochemical filter (35) with a constant voltage. System (10) according to any one of claims 7 to 9, wherein the fluidic control device (43) is a valve. The system (10) of any one of claims 7 to 10, further comprising a check valve (45) downstream of the cathode valve (42), configured to allow the second gas to flow from the cathode valve (42) to the cell cathode outlet (24), without allowing the second gas to flow from the cell cathode outlet (24) to the cathode valve (42).

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